1. Field of the Invention
This invention relates in general to air conditioning devices and more particularly to an air conditioning device which utilizes evaporative cooling in an indirect regenerative manner to cool air.
2. Description of the Prior Art
Devices which cool air by evaporation have been used for many years as a relatively inexpensive way to cool air and a multiplicity of such devices, generally referred to as "evaporative coolers" have been devised and marketed which utilize this well known principle. In general, evaporative coolers mix water directly with warm and relatively dry ambient air and the resulting evaporation reduces the sensible heat of the air which is delivered to a point of use.
In the most commonly used evaporative coolers, the warm and relatively dry ambient air is drawn at a relatively high velocity through wettable excelsior pads, by an air moving device provided within a cabinet. The sensible heat of the air moved into the cabinet in this manner is reduced and the same air moving device is operated to deliver the cooled air into a building, usually by means of a duct system.
Another prior art device of this same general type injects moisture directly into the incoming warm and relatively dry ambient air by spraying a fine mist into the air.
There are several factors which effect the operating efficiency of evaporative coolers, such as dry bulb temperature, wet bulb temperature, and the relative humidity of the ambient air, velocity of the air, and the like. However, in general, evaporative coolers of the above described type are very effective and work best when the relative humidity of the ambient air to be cooled thereby is low and they decrease in efficiency as the relative humidity increases.
As is well known in the art, the evaporative cooling phenomenon is an adiabatic process in that it occurs without any gain or loss in wet bulb temperature which is a reflection of the total heat content of the air. When evaporation occurs, the sensible heat, or dry bulb temperature, of the air is lowered in proportion to the rise of the latent heat of the moisture in the air and this lowering of the dry bulb temperature is dependent on the evaporation rate. When the evaporation rate is low due to the ambient air having a relatively high humidity to start with, the drop in dry bulb temperature of the air is low. The overall result of this is that under atmospheric conditions wherein the air to be cooled has a high relative humidity, the air delivered by the prior art evaporative coolers is uncomfortably hot and humid.
One existing alternative to evaporative coolers are the well known refrigeration type of air conditioning mechanisms which operate on a heat exchange principle wherein the total heat content of the air being treated is reduced by placing it in indirect heat exchange relationship with a refrigerant. Such mechanisms are not effected by the relative humidity and thus are effective at all times. However, refrigeration air conditioning devices of this type are considerably more expensive to purchase and operate than are evaporative coolers, and are becoming increasingly costly to operate as the cost of electricity increases.
For these reasons, it has become a common practice in hot and arid climates to use the relatively inexpensive prior art evaporative coolers when they produce relatively comfortable conditioned air, and switch over to the refrigeration type of air conditioning mechanism during periods when the effectiveness of those evaporative coolers falls below acceptable levels. The high and ever increasing costs of electricity, however, has resulted in many people being unwilling, and in many cases unable, to operate the more expensive refrigeration mechanisms.
One further alternative known to me has been suggested, and has been fully described in U.S. Pat. No. 4,023,949 which issued on May 17, 1977 to L. A. Schlom et al. Briefly, this prior art patent discloses an evaporative refrigeration system wherein fresh ambient air is drawn through the dry side of a heat exchanger, the wet side of which is cooled by evaporation. The passage of incoming air through the heat exchanger extracts heat from the air and the cooled air is directed through ducts of the disclosed system to a load, e.g. a room, to be cooled. As the cooled air passes through the load, it will absorb some of the heat from the load, and that air is returned by ducts, also a part of the system, to a blower compartment of the system. A centrifugal blower is provided in the blower compartment to direct the returned air to the wet side of the heat exchanger where it interacts with a water spray to evaporatively cool the wet side of the heat exchanger. A portion of the cooled air emerging from the dry side of the heat exchanger may be selectively mixed with the return air in the blower compartment. Also, a portion of the return and/or selectively mixed air may be selectively directed into the incoming air movement path as it starts its movement through the dry side of the heat exchanger. The Schlom et al patent also provides an annular duct structure which surrounds the incoming air inlet duct of the system to precool the incoming ambient air. The evaporatively cooled exhaust air emerging from the wet side of the heat exchanger is passed through the annular chamber to accomplish pre-cooling of the incoming ambient air.
The prior art patent of Schlom et al utilizes what may be described as an indirect regenerative technique for reducing the total heat content of the air being cooled in an attempt to produce lower temperatures in the air than can be produced by the conventional evaporation technique alone, and to produce such lowered temperatures without adding moisture to the air. While the Schlom et al patent appears to be an improvement over the conventional evaporative cooler, it is using the wrong air. The air returning from the load is relatively warm due to its having passed through the load and is therefore at a considerably warmer temperature in comparison to the cooled air emerging from the dry side of the heat exchanger. As a result of this, the evaporation process used to cool the wet side of the heat exchanger will not be as efficient as it could be if cooled air emerging from the dry side of the heat exchanger were used exclusively. When the temperature differential across the heat exchanger is less than maximum, the heat exchange capabilities are less than maximum. Even if a portion of the cooled air emerging from the dry side of the heat exchanger is mixed with the return air, the resultant air will still not be at the lowest possible temperature due to the mixing.
Therefore, a need exists for a new and improved air conditioning device which overcomes some of the problems and shortcomings of the prior art.